Fire-resistant or -retardant materials are used as interior finishes for buildings, ships and vehicles. Also, emergency equipment, such as standby generators or batteries, are protected by fire walls to ensure that they can continue functioning during a fire, at least temporarily. The fire walls are usually provided with one or more through-holes by which electrical cables pass to and from the emergency power source. These through-holes are seldom completely filled by the cables, leaving some free air-space in the through-hole. In a fire, smoke and flames will pass through such an air space to the inside of the fire wall, and consequently burn the emergency equipment. To prevent passage of smoke, heat and flame, such air spaces have been closed off with nonflammable plates or blocks at the ends of the through-holes or have been filled with nonflammable fibers. However, these conventional techniques do not always provide satisfactory fire and smoke protection. Sometimes, the air space is filled with concrete, but the resulting necessity of breaking away the concrete makes the installation of additional cables inconvenient. Because of these difficulties, there is a need for improved ways of sealing such through-holes.